Pigment dispersion, inkjet composition, ink set, and recording device

ABSTRACT

A pigment dispersion containing a metal pigment, wherein the metal pigment contains plate-like particles, and in the case where the longitudinal diameter on the planar surface of the plate-like particle is X, the lateral diameter is Y, and the thickness is Z, the 50% average particle diameter R50 of a corresponding circle determined from the surface area in the X-Y plane of the plate-like particle is between 0.5 and 3 μm, and the condition R5O/Z&gt;5 is satisfied.

CROSS-REFERENCE TO RELATED APPLICATIONS

The entire disclosure of Japanese Patent Application No. 2006-340894,filed on Dec. 19, 2006, No. 2006-340899, filed on Dec. 19, 2006, and No.2007-210976, filed on Aug. 13, 2007, is expressly incorporated byreference herein.

BACKGROUND

1. Technical Field

The present invention relates to a pigment dispersion, ink composition,ink set, and recording device, and particularly relates to a pigmentdispersion, ink composition, ink set, and recording device which canform an image with metallic gloss.

2. Related Art

Conventionally, gold bronze powder made of brass and aluminum finepowders and the like, printing ink with silver powder pigment, foilpress printing using metal foil, and a thermal transfer method using ametal foil have been used to form a coating film with metallic gloss ofprinted matter.

However, with a coating film consisting of a printing ink that uses goldbronze powder, or silver powder, the average particle size of the metalpowders that are used will be large, between 10 μm and 30 μm, and thus aflat metallic gloss finish can be obtained, but achieving a mirror glossis difficult. Furthermore, with the foil press or thermal transfermethods that use a metallic foil, an adhesive is applied as a printingmedium, and a flat metallic foil is pressed thereon, the recordingmedium and the metallic foil are heated to cause firm adhesion, and themetal foil and recording medium are thermally welded together.Therefore, a relatively good gloss can be achieved, but there are manymanufacturing steps, and pressure and heat are applied during themanufacturing process, so the recording medium is restricted to thelimited recording media that are resistant to heat and deformation.

In recent years, many examples of applying inkjet technology to printinghave been seen, and one example of this application is metallicprinting. For example, JP-A-2002-179960 discloses technology of forminga metal film on the surface of plastic spherical particles, and printingan ink composition that contains a pigment using inkjet printing.However, in order to obtain a highly metallic gloss, the spheres must bedeformed and flattened to make a smooth surface, and with thistechnology, heating and pressing with a roller must be simultaneouslyperformed. Therefore, the equipment and manufacturing processes areinevitably complicated by this point, and the recording medium is alsorestricted.

Furthermore, JP-A-2003-292836 and JP-A-2003-306625 disclose technologythat uses an ink composition wherein a colloid of a precious metal suchas gold or silver is dispersed. However, if the particle size of theprecious metal colloid is small, within a range between severalnanometers and several tens of nanometers in order to give priority todispersion and stability, discoloration caused by plasmon absorptionwill occur, and the ink composition will not provide a metallic gloss.In this case, after the coating film is dried, a metallic gloss isachieved by heating to a temperature of 150° C. or higher in order tofuse the colloid particles together. In addition, even if a metallicgloss can be achieved with these technologies, achieving a surface witha mirror surface metallic gloss where the specular gloss at 20°, 60°,and 85° exceeds 200, 200, and 100, respectively on a uniform surfacewithout variation is difficult. Furthermore, if the particle size isincreased in order to give priority to metallic gloss, the dispersionstability will be degraded, and problems with conglomeration andsettling will be inevitable, and the storage life of the ink compositionwill be significantly reduced. Furthermore, although trivial, usingprecious metals as a material will increase the cost of the inkcomposition, so use will be restricted to applications with high addedvalue, and there are disadvantages related to cost.

SUMMARY

An advantage of some aspects of the invention is the ability to providea pigment dispersion with a high metallic mirror gloss using aluminum asa relatively inexpensive metal material, as well as to an inkcomposition, and recording device. Furthermore, another advantage ofsome aspects of the invention is the ability to provide an ink setcapable of forming a coating film with different metallic gloss ofprinted matter by containing an ink set that includes ink compositionswith different concentrations of metal pigments.

As result of diligent research, the present inventors have discoveredthat printed matter with a high mirror gloss which was heretoforeunattainable can be obtained by using a metal pigment dispersion, inkcomposition, ink set and recording device that use specific metalpigments. The present invention is based on these findings, and providesthe following inventions.

(1) A pigment dispersion comprising a metal pigment, wherein the metalpigment contains plate-like particles, and in the case where thelongitudinal diameter on the planar surface of the plate-like particleis X, the lateral diameter is Y, and the thickness is Z, the 50% averageparticle diameter R50 of a corresponding circle determined from thesurface area in the X-Y plane of the plate-like particle is between 0.5and 3 μm, and the condition R50/Z>5 is satisfied.

(2) The pigment dispersion according to (1), wherein the maximumparticle diameter Rmax of a corresponding circle determined from thesurface area in the X-Y plane of the plate-like particle is 10 μm orless;

(3) The pigment dispersion according to (1), wherein the metal pigmentis aluminum or an aluminum alloy;

(4) The pigment dispersion according to (1), wherein the metal pigmentis made by crushing a metal deposition film;

(5) The pigment dispersion according to (1), wherein the particle sizedistribution CV value of the metal pigment as determined by thefollowing equation is 60 or less;

CV value=standard deviation of particle size distribution/averageparticle diameter×100;   Equation 1

(6) An ink composition, comprising: the pigment dispersion according toany one of (1) through (5), an organic solvent, and a resin;

(7) The ink composition according to (6), wherein the concentration ofthe metal pigment in the ink composition is between 0.1 and 3.0 wt %;

(8) The ink composition according to (6), wherein the organic solventincludes one or more types of alkylene glycol ether that is a liquid atambient temperature and pressure;

(9) The ink composition according to (6), wherein the organic solvent isa blend of an alkylene glycol diether, an alkylene glycol monoether, anda lactone;

(10) The ink composition according to (6), wherein the resin is at leastone type of resin selected from a group consisting of polyvinyl butyral,cellulose acetatobutyrate, and polyacryl polyol;

(11) The ink composition according to (6), further comprising at leastone type of acetylene glycol based surfactant and/or silicone basedsurfactant;

(12) The ink composition according to (6), wherein when applied to aninkjet recording device that satisfies the condition of L≧5W where L μmis the nozzle diameter of an inkjet head and W μm is the size of a meshfilter opening provided in an ink flow path, the number of plate-likeparticles where the average particle diameter R μm of a correspondingcircle determined from the surface area in the X-Y plane of theplate-like particles satisfies the condition R>(L/5) is no more than 5%of the total number of plate-like particles;

(13) An ink set, comprising a plurality of the ink compositionsaccording to any one of (1), wherein each of the ink compositions has adifferent concentration of metal pigment;

(14) The ink set according to (13), wherein the concentration of a metalpigment in at least one of the ink compositions is 0.1 wt. % or higherand less than 1.5 wt. %, and the concentration of a metal pigment in atleast one of the other ink compositions is 1.5 wt. % or higher and 3.0wt % or less;

(15)A recording device, comprising the ink set according to (13).

According to an aspect of the invention, an image with a high metalgloss (so-called metallic gloss) which was heretofore unobtainable canbe obtained on a recording medium by using a metal pigment with aspecific shape and restricted particle diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective diagram for describing theconstruction of the recording head; and

FIG. 2 is a cross section diagram for describing the construction of theink insertion needle.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Pigment Dispersion

The pigment dispersion of this aspect is a pigment dispersion thatcontains a metal pigment (hereinafter also referred to as “metallicpigment”), and this metallic pigment contains plate-like particles madeby crushing a metal deposition film, and in the case where thelongitudinal diameter on the planar surface of the plate-like particleis X, the lateral diameter is Y, and the thickness is Z, the 50% averageparticle diameter R50 of a corresponding circle determined from thesurface area in the X-Y plane of the plate-like particle is between 0.5and 3 μm, and the condition R50/Z>5 is satisfied.

The term “plate-like particle” refers to a particle which hasessentially a flat surface (X-Y plane) and essentially a uniformthickness (Z). The plate-like particles are made by crushing a metaldeposition film, and therefore metal particles with essentially a flatsurface and essentially a uniform thickness can be obtained.Furthermore, the longitudinal diameter, lateral diameter, and thicknessof the plate-like particle can be defined as X, Y. and Z respectively.

The term “diameter of a corresponding circle” refers to the diameter ofan imaginary circle which has the same projected surface area as theprojected surface area on the essentially flat surface (X-Y plane) ofthe plate-like particles of the metallic pigment. For example, if theessentially flat surface (X-Y plane) of the plate-like particles of themetallic pigment is polygonal, the diameter of the corresponding circleof the plate-like particle of metallic pigment is the diameter of thecircle obtained by converting the projected area of that polygon to acircle.

The 50% average particle diameter R50 of a corresponding circledetermined using the surface area of the X-Y plane of the plate-likeparticles is preferably between 0.5 and 3 μm, and more preferablybetween 0.75 and 2 μm, from the perspective of metallic gloss andprinting stability. If the 50% average particle diameter R50 is lessthan 0.5 μm, the gloss will be insufficient. On the other hand, if the50% average particle diameter R50 exceeds 3 μm, the printing stabilitywill be poor.

Furthermore, the relationship between the 50% average particle diameterR50 of a corresponding circle and the thickness Z is preferably suchthat R50/Z>5, from the perspective of ensuring high metal gloss. IfR50/Z is 5 or less, there will be a problem with insufficient metalgloss.

The maximum particle diameter Rmax of a corresponding circle determinedfrom the area of the plate-like particle in the X-Y plane is preferably10 μm or less from the perspective of preventing the ink compositionfrom plugging the inkjet recording device. If Rmax is 10 μm or less,plugging of the nozzle in the ink jet recording device and a mesh filteror the like provided in the ink flow path can be prevented.

The metallic pigment is preferably aluminum or an aluminum alloy, from aperspective of cost and a perspective of ensuring metal gloss. If analuminum alloy is used, the other metal elements or non-metal elementsthat can be added to the aluminum are not particularly restricted solong as the element has a function that provides metal gloss or thelike, but silver, gold, platinum, nickel, chrome, tin, zinc, indium,titanium, and copper and the like can be suggested, and these elementscan be favorably used individually, or as an alloy, or as a mixture ofat least one type of element.

The method of manufacturing the metallic pigment is to peel theinterface between a metal or alloy layer and a peeling resin layer froma sheet substrate of a composite pigment source with a structure where apeeling resin layer and a metal or alloy layer are successively overlaidonto a sheet substrate surface, followed by crushing and pulverizing toobtain plate-like particles. Furthermore, in the case where thelongitudinal diameter on the planar surface of the plate-like particleis X, the lateral diameter is Y, and the thickness is Z, the 50% averageparticle diameter R50 of a corresponding circle determined from thesurface area in the X-Y plane of the plate-like particle obtained isbetween 0.5 and 3 μm, and the condition R50/Z>5 is satisfied.

The longitudinal diameter X, lateral diameter Y, and the diameter of acorresponding circle on the surface of the metallic pigment (plate-likeparticle) can be measured using a particle image analyzer. For example,a flow type particle image analyzer FPIA-2100, FPIA-3000, or FPIA-3000Smanufactured by Sysmex Corporation can be used as a the particle imageanalyzer.

The particle distribution (CV value) of the metallic pigment (plate-likeparticles) is determined by the following equation.

CV value=standard deviation of particle size distribution/averageparticle diameter×100   Equation 1

Here, the CV value obtained is preferably 60 or less, more preferably 50or less, and even more preferably 40 or less. Excellent printingstability can be achieved by selecting a metallic pigment where the CVvalue is 60 or less.

The metal or alloy layer is preferably made using vacuum deposition, ionplating, or sputtering.

The thickness of the metal or metal alloy is 20 nm or higher and 100 nmor less. Thereby a pigment with an average thickness of 20 nm or higherand 100 nm or less can be obtained. If the average thickness is 20 nm orgreater, the pigment will have excellent reflectivity and brightness,and will have good properties as a metallic pigment. If the averagethickness is 100 nm or less, the increase of the apparent specificgravity can be suppressed to thereby ensure the dispersion stability ofthe metallic.

The peeling resin layer of the composite pigments source is an undercoatlayer under the metal or alloy layer, and is a peeling layer forincreasing the peeling properties to the sheet substrate surface. Theresin that is used as the resin peeling layer is preferably a polyvinylalcohol polyvinyl butyral, polyethylene glycol, polyacrylic acid,polyacrylamide, cellulose derivative, acrylate polymer, or modifiednylon resin.

A solution containing a mixture of one or more of the aforementionedresins is applied to the recording medium, and a layer is formed bydrying or the like. The application solution can contain an additivesuch as a viscosity adjusting agent.

The peeling resin layer can be formed using commonly used gravureapplication, roller application, blade application, extrusionapplication, dip application, or spin coat method or the like. Afterapplying and drying, the surface can be smoothed by calendaring ifnecessary.

The thickness of the peeling resin layer is not particularly restricted,but is preferably between 0.5 and 50 μm, and more preferably between 1and 10 μm. If the thickness is less than 0.5 μm, the amount ofdispersion resin will be insufficient, and if the thickness is greaterthan 50 μm, peeling at the interface with the pigment layer will readilyoccur when rolled.

The sheet substrate is not particularly restricted, but can be apolyester film such as polytetrafluoroethylene, polyethylene,polypropylene, and polyethylene terephthalate, a polyamide film such as66-nylon and 6-nylon, or a peeling film such as a polycarbonate film,triacetate film, or polyamide film, or the like. Preferably, the sheetsubstrate is made of polyethylene terephthalate or a copolymer thereof.

The thickness of the sheet substrate is not particularly restricted, butis preferably between 10 and 150 μm. If the thickness is 10 μm orgreater, handling problems such as processing will not occur, and if thethickness is 150 μm or less, the flexibility will be excellent, andproblems will not occur when rolled or peeled or the like.

Furthermore, the metal or alloy layer can be enclosed between protectivelayers as shown in JP-A-2005-68250. The protective layer can be asilicon oxide layer or. a protective resin layer.

The silicon oxide layer is not particularly restricted so long as thelayer contains silicon oxide, but is preferably formed from a siliconalkoxide such as tetraalkoxysilane, or polymer thereof.

The silicon oxide layer film is formed by applying a solution of siliconalkoxide or polymer thereof dissolved in alcohol, and then baking.

The protective resin layer is not particularly restricted so long as theresin does not dissolve in the dispersion solvent, and examples includepolyvinyl alcohol, polyethylene glycol, polyacrylic acid,polyacrylamide, or a cellulose derivative, and is preferably a polyvinylalcohol or a cellulose derivative.

An aqueous solution containing a mixture of one or more of theaforementioned resins is applied, and a layer is formed by drying or thelike. The application solution can also contain additives such as aviscosity adjusting agent.

Application of the silicon oxide and resin is performed by the samemethod as application of the peeling resin layer.

The thickness of the protective layer is not particularly restricted,but is preferably in a range between 50 and 150 nm. If the thickness isless than 50 nm, the mechanical strength will be insufficient, but ifthe thickness exceeds 150 nm, the strength will be too high, so crushingand dispersing will be difficult, and peeling will occur at theinterface with the metal or alloy layer.

Furthermore, a layer of colored material can be placed between the“protective layer” and the “metal or alloy layer”, as shown inJP-A-2005-68251.

The colored layer is added to obtain a composite pigment of any color,and the materials are not particularly restricted so long as the coloredmaterial can provide an arbitrary color or hue, in addition to the metalgloss and brightness of the metallic pigment of the invention. Thecolored material used in the colored layer can be either a pigment ordye. Furthermore, any commonly used pigment or dye can be suitably used.

In this case, the “pigment” that is used in the colored layer refers toa natural pigment, synthetic organic pigment, or synthetic inorganicpigment or the like as generally defined in the field of pigmentchemistry, and is different than the “composite pigment” of theinvention formed with a multilayer structure.

The method of forming the colored layer is not particularly restricted,but is preferably formed by coating.

Furthermore, if the colorant that is used in the colored layer is apigment, a resin for dispersing the colorant is preferably included, andthe resin for dispersing the colorant is preferably made by dispersingor dissolving a pigment, a resin for dispersing the colorant, and otheradditives if necessary, in a solvent, forming a uniform liquid layer byspin coating this solution, and then drying to make a thin resin film.

Note, when manufacturing the composite pigment source, both the coloredlayer and the protective layer are preferably formed by coating in orderto improve productivity.

The composite pigment source may also have a layered construction with aplurality of multilayered structures of successive peeling resin layers,metal or alloy layers, and protective layers. At this time, the totalthickness of the multilayer structure containing a metal or alloy layer,or in other words the thickness of metal or alloy—peeling resinlayer—metal or alloy layer, or the peeling resin layer—metal or alloylayer is preferably 5000 nm or less. If the thickness is 5000 nm orless, cracking and peeling will not easily occur even if the compositepigment source is rolled in a roll, so the storage properties will beexcellent. Furthermore, when a pigment is formed, the pigment will befavorable, with excellent brightness.

Furthermore, a structure containing multiple successive layers of apeeling resin layer and a metal or an alloy layer on both sides of thesheet substrate surface can be suggested, but this is not a restriction.

The method of peeling from the sheet substrate is not particularlyrestricted, but a method of immersing the composite pigment source in aliquid, or a method of immersing in a liquid while simultaneouslyapplying ultrasonic waves, peeling, and then crushing the peeledcomposite pigment are preferable.

With the pigment obtained as described above, the peeling resin layeralso acts as a protective colloid, and therefore a stable dispersion canbe obtained simply by dispersing in a solvent. Furthermore, with the inkcomposition that uses this pigment, the resin derived from the peelingresin layer also functions to provide adhesion to the recording medium,such as paper.

Ink Composition

The ink composition of this aspect contains the aforementioned metallicpigment, organic solvent, and resin.

The concentration of metallic pigment in the ink composition ispreferably between 0.1 and 3.0 wt %, more preferably between 0.25 and2.5 wt %, and even more preferably between 0.5 and 2 wt %, if only onetype of metallic ink is used in the ink set.

Concerning the concentration of metallic pigment in the ink compositionif a plurality of metallic ink compositions are in the ink set, thecomposition of metal pigment in at least one type of the aforementionedink compositions is preferably 0.1 wt. % or higher and less than 1.5 wt.%, and the concentration of metal pigment in at least one of the otherink compositions is preferably 1.5 wt. % or higher and 3.0 wt % or less.

If the concentration of metallic pigment in the ink composition is 0.1wt % or higher and less than 1.5 wt %, a half mirror gloss surface, orin other words a glossy feel can be achieved by spraying an amount ofink that does not sufficiently cover the printing surface, but printingon a texture where the background appears to be transparent will bepossible, and a metal glossy surface with high gloss can be formed byspraying sufficient ink to cover the printing surface. Therefore, thisis suitable for forming a half mirror image on a transparent recordingmedium, or for providing a metal gloss surface with high gloss.Furthermore, if the concentration of metallic pigment in the inkcomposition is 1.5 wt % or higher and 3.0 wt % or lower, the metalpigment will be randomly arranged on the printing surface, so a highgloss will not be achieved and a metal gloss surface with a matte finishcan be formed. Therefore, this is suitable for forming a shielding layeron a transparent recording medium.

The organic solvent is preferably a polar organic solvent, and examplesinclude alcohols (such as methyl alcohol, ethyl alcohol, propyl alcohol,butyl alcohol, isopropyl alcohol, or fluorodated alcohol and the like),ketones (such as acetone, methylethyl ketone, and cyclohexanone and thelike), carboxylate esters (such as methyl acetate, ethyl acetate, propylacetate, butyl acetate, methyl propionate, and ethyl propionate and thelike), and ethers (such as diethyl ether, dipropyl ether,tetrahydrofuran, and dioxane, and the like).

In particular, the organic solvent preferably contains one or more typesof an alkylene glycol ether that is a liquid at ambient temperature andpressure.

The alkylene glycol ether can be an ethylene glycol based ether orpropylene glycol based ether which contains a methyl, n-propyl,i-propyl, n-butyl, i-butyl, hexyl, or 2-ethyl hexyl resin group and anallyl or phenyl group having a double bond as a base. These alkyleneglycol ethers are colorless with little odor, and have an ether groupand a hydroxyl group in the molecule, and therefore demonstrate theproperties of both alcohols and ethers, and are liquid at roomtemperatures. Furthermore, these alkylene glycol ethers can bemonoethers where only one of the hydroxyl groups have been substituted,or can be diethers, where both of the hydroxyl groups have beensubstituted, and furthermore a plurality of types can be combined andused together.

In particular, the organic solvent is preferably a blend of an alkyleneglycol diether, an alkylene glycol monoether, and a lactone.

Examples of the alkylene glycol monoether include ethylene glycolmonomethyl ether, ethylene glycol monoethyl ether, ethylene glycolmonoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycolmonohexyl ether, ethylene glycol monophenyl ether, diethylene glycolmonomethyl ether, diethylene glycol monoethyl ether, diethylene glycolmonobutyl ether, diethylene glycol dimethyl ether, diethylene glycoldiethyl ether, triethylene glycol monomethyl ether, triethylene glycolmonoethyl ether, triethylene glycol monobutyl ether, tetraethyleneglycol monomethyl ether, tetraethylene glycol monoethyl ether, propyleneglycol monomethyl ether, propylene glycol monomethyl ether, dipropyleneglycol monomethyl ether, dipropylene glycol monoethyl ether, and thelike.

Examples of alkylene glycol diethers include ethylene glycol dimethylether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether,diethylene glycol dimethyl ether, diethylene glycol diethyl ether,diethylene glycol dibutyl ether, triethylene glycol dimethyl ether,triethylene glycol diethyl ether, triethylene glycol dibutyl ether,tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether,tetraethylene glycol dibutyl ether, propylene glycol dimethyl ether,propylene glycol diethyl ether, dipropylene glycol dimethyl ether,dipropylene glycol diethyl ether, and the like.

Furthermore, the lactone can be γ-butyrolactone, δ-valerolactone, orε-caprolactone and the like.

The objective of the present invention can be better achieved by usingone of the aforementioned favorable constructions.

The resin that is used in the ink composition is for example an acrylicresin, a styrene-acrylic resin, a rosin modified resin, a terpene basedresin, a polyester resin, a polyamide resin, an epoxy resin, avinylchloride resin, a vinylchloride-vinylacetate copolymer, a fiberbased resin (such as cellulose acetate buterate, hydroxypropylcellulose), polyvinyl butyral, polyacrylic polyol, polyvinyl alcohol,and polyurethane and the like.

Furthermore, fine particles of a nonaqueous dispersion polymer can alsobe used as the resin. These are dispersions where fine particles ofpolyurethane resin, acrylic resin, acrylic polyol resin or the like arestably dispersed in an organic solvent.

Examples include polyurethane resins such as Sanprene IB-501 andSanprene IB-F370, manufactured by Sanyo Chemical Industries, Ltd., andacrylicpolyol resins such as N-2043-60MEX and N-2043-AF-1 manufacturedby Harima Chemicals, Inc.

The amount of resin emulsion added to the ink composition is preferably0.1 wt % or higher and 10 wt % or lower, in order to further increasethe adhesion of the pigment to the recording medium. If the amount addedis excessive, printing stability will not be achieved, but ifinsufficient, adhesion will be insufficient.

The ink composition preferably contains at least one type of glycerin,polyalkylene glycol, or sugar. The amount of at least one type ofglycerin, polyalkylene glycol, or sugar that is added to the inkcomposition is preferably 0.1 wt % or higher and 10 wt % or lower.

With this type of preferred construction, drying of the ink can besuppressed, plugging can be prevented, spraying of the ink can bestabilized, and the image quality of the recorded matter can befavorable.

The polyalkylene glycol is a linear polymer compound with a constructionof repeating ether bonds in the main chain, and is produced for exampleby ring opening polymerization of a cyclic ether.

Specific examples of polyalkylene glycol include polymers such aspolyethylene glycol and polypropylene glycol, ethylene oxide-propyleneoxide copolymer and derivatives thereof. The copolymer can be any typeof copolymer such as a random copolymer, block copolymer, graftcopolymer, or alternating copolymer.

Preferable examples of a polyalkylene glycol include those expressed bythe following formula.

HO—(CnH₂nO)m-H

(In the above formula, n represents an integer between 1 and 5, and mrepresents an integer between 1 and 100.)

Note, in the formula, (CnH₂nO)m can have a single value for n or canhave a combination of two or more values within the range of integer n.For example, the term becomes (C₃H6O)m if n is 3, or becomes(CH₂O—C₄H₈O)m if n is a combination of 1 and 4. Furthermore, the integerm can be a single constant or a combination of two or more constantswithin the aforementioned range. For instance, in the above example, ifm is a combination of 20 and 40, the term becomes (CH₂O)₂₀—(C₂H₄O)₄₀,and if m is a combination of 10 and 30, the term becomes(CH₂O)₁₀—(C₄H₈O)₃₀. Furthermore, the integers n and m can be in anycombination with in the aforementioned ranges.

The sugar can be a simple sugars such as pentose, hexose, heptose,octose, a polysaccharide such as a disaccharide, trisaccharide, ortetrasaccharide, as well as derivatives thereof such as sugar alcohols,reduced derivatives such as deoxy acids, oxidized derivatives such asaldonic acid and uronic acid, dehydrated derivatives such as glycoseen,as well as amino acids and thiosugars and the like. Polysacchariderepresent a wide range of saccharides, and include substances widelyfound in nature such as alginic acid, dextrin, and cellulose.

The ink composition preferably contains at least one type of acetyleneglycol based surfactant and/or silicone based surfactant. The amount ofsurfactant added is preferably 0.01 wt % or higher and 10 wt % or lower,based on the amount of pigment in the ink composition.

With this preferred construction, the wettability of the ink compositiontowards the recording medium will be improved, and rapid adhesion can beachieved.

Preferred examples of the acetylene glycol based surfactant includeSurfinol 465 (trademark), Surfinol 104 (trademark) (product trade names,manufactured by Air Products and Chemicals Inc.), Olfin STG (trademark),Olfin E1010 (trademark) (product trade names, manufactured by NissinChemical Industry Co., Ltd.), and the like.

Preferred examples of the silicone surfactant include polyester modifiedsilicone and polyether modified silicone. Specific examples includeBYK-347, BYK-348, BYK-UV3500, BYK-UV3570, BYK-UV3510, and BYK-UV3530(manufactured by BYK Japan).

The ink composition can be prepared by a commonly known and used method.For example, the aforementioned metallic pigment, dispersing agent, andsolvent are first blended together and then a pigment dispersion isprepared using a ball mill, bead mill, ultrasonic waves, or jet mill orthe like, in order to achieve the desired ink characteristics.Furthermore, a pigment ink composition can be obtained by adding abinder resin, solvent, and other additives (such as dispersion assistingagents and viscosity adjusting agents) while mixing.

In addition, the composite pigment source is ultrasonically treated in asolvent to make a composite pigment dispersion, and then the necessaryink solvents can be blended, or the composite pigment source can beultrasonically treated in the ink solvent to directly make the inkcomposition.

The physical properties of the ink composition are not particularlyrestricted, but for example the surface tension is preferably between 20and 50 mN/m. If the surface tension is less than 20 mN/m, the inkcomposition will spread out on the surface of the inkjet recordingprinter head, or will smear, and spraying ink droplets will bedifficult. On the other hand, if the surface tension exceeds 50 mN/m,the ink composition will not spread out on the surface of the recordingmedium, and favorable printing will not be possible.

Ink Set

The ink set of this aspect contains a plurality of the aforementionedink compositions, and each of the ink compositions has a differentconcentration of metal pigment.

Preferably, the concentration of metal pigment in at least one of theink compositions is 0.1 wt. % or higher and less than 1.5 wt. %, and theconcentration of metal pigment in at least one of the other inkcompositions is 1.5 wt. % or higher and 3.0 wt % or less.

Recording Device

The recording device of this aspect is an inkjet recording devicecontaining the aforementioned ink set, or the like.

The construction of the recording head 3 of the inkjet recording devicewill be described next. FIG. 1 is a schematic perspective view of arecording head 3 as stored in a carriage (not shown in the drawings).Furthermore, FIG. 2 is a cross-section view of an ink insertion needle19 that is inserted into the ink cartridge.

The recording head 3 that is shown has a cartridge base 15 (hereinafterreferred to as “base”). The base 15 is attached to a head case 16. Theleading edge of the head case 16 is attached to (equipped with) a flowpath unit 17. The base 15 is molded of a synthetic resin, and aplurality of partitions 15′ (liquid storage member devices) are providedon the top surface thereof.

Each of the partitions 15′ is attached to an ink insertion needle 19through a mesh filter 18. Furthermore, the partitions 15′ are equippedwith an ink cartridge (not shown in the drawings). In other words, theink cartridges are located on the base 15. The details of the inkinsertion needles 19 that are inserted into the ink cartridges will bedescribed later.

A circuit board 20 is attached to other surface of the base 15 oppositeto the partitions 15′. Furthermore, this circuit board 20 is attached tothe base 15 via a sheet material 21 which acts as packing.

The head case 16 is fixed to the base 15, and is a casing for storing anoscillating unit 22 which contains a piezoelectric oscillating element.Furthermore, a flow path unit 17 is attached with adhesive or the liketo the leading edge surface on the opposite side as the base 15 mountingsurface of the head case 16. This flow path unit 17 is layered with anelastic plate 23, a flow path forming board 24, and a nozzle plate 25,in succession, and is formed by securing and integrating the layerstogether with an adhesive or the like.

The nozzle plate 25 is a plate-like member made from a thin stainlesssteel plate, and has fine nozzle openings 26 arranged in the line at apitch corresponding to the dot forming density of the printer.Furthermore, the head cover 27 is formed for example from a thin platemember made of metal.

The ink insertion needle 19 that is inserted into the ink cartridge is ahollow needle formed as a conical form at the tip end to the upstreamside as shown in FIG. 2, while the inside forms an ink insertion path41. The bottom part has a taper form that is wider on the upstream sidethan the downstream side. Furthermore, the leading edge of the inkinsertion needle 19 has an ink insertion hole 42 that connects theoutside space with the ink insertion flow path 41.

The ink insertion needle 19 is attached to the base 15 with a meshfilter 18 therebetween using ultrasonic welding for example. Thereby theink insertion path 41 of the ink insertion needle 19 and the inkconnecting flow path 37 of the head case 16 can be connected.

Furthermore, when the ink cartridge (not shown in the drawings) is setin a partition 15′ of the base 15, the ink insertion needle 19 will beinserted into the ink insertion opening of the ink cartridge, and theinside cavity of the ink cartridge will be connected through the inkinsertion hole 42 to the ink insertion path 41 in the ink insertionneedle 19. Next, the ink that is stored in the ink cartridge passesthrough the ink insertion hole 42, enters the ink insertion path 41,passes through the ink connecting flow path 37, and is sprayed from thenozzle opening 26.

If the diameter of the nozzle opening 26 in the recording head 3 of theinkjet recording device is L μm, and the size of the openings in themesh filter 18 provided in the ink insertion path 41 is W μm, therelationship between the nozzle diameter L μm and the mesh filteropening size W μm is preferably such that L≧5W. If an ink compositionthat includes a pigment dispersion of this aspect is used in an inkjetrecording device which satisfies this relationship, plugging of thenozzle opening 26 by the metallic pigment can be prevented. Furthermore,from a perspective of ensuring spraying stability of the inkcomposition, if the average particle diameter as determined from thediameter of a corresponding circle with the same surface area as the X-Yplane is R μm, the number of plate-like particles which satisfy thecondition of R>(L/5) is preferably 5% or less of the total number ofplate-like particles.

The ink composition of the present invention can be used for recordingby spraying droplets thereof and causing those droplets to adhere to arecording medium.

From the viewpoint of angular dependency, an image is preferably formedwhere the measurement values for the specular gloss of the recordingmedium at angles of 20°, 60°, and 85° as defined by JIS Z 8741 aresimultaneously no less than 200, 200, and 100, more preferably themeasurement values for the specular gloss of the recording medium atangles of 20°, 60°, and 85° as defined by JIS Z 8741 are simultaneouslyno less than 400, 400, and 100, and even more preferably the measurementvalues for the specular gloss of the recording medium at angles of 20°,60°, and 85° as defined by JIS Z 8741 are simultaneously no less than600, 600, and 100.

An image which has measured values for the specular gloss of therecording medium at angles of 20°, 60°, and 85° as defined by JIS Z 8741are simultaneously no less than 200 or higher but less than 400, 200 orhigher but less than 400, and 100 or higher, respectively, will have ametallic gloss that is a flat gloss finish (matte finish).

An image which has measured values for the specular gloss of therecording medium at angles of 20°, 60°, and 85° as defined by JIS Z 8741are simultaneously no less than 400 or higher but less than 600, 400 orhigher but less than 600, and 100 or higher, respectively, will have ametallic gloss that is has some shine to the degree that an objectreflected in the image that is formed will be somewhat distinguishable.

A metallic glossy image with measured values for the specular gloss atangles of 20°, 60°, and 85° as defined by JIS Z 8741 are simultaneously600 or higher, 600 or higher, and 100 or higher, respectively, will besharp, and will have a metallic gloss that has so-called “mirror gloss”to the degree that an object reflected in the image that is formed willbe clearly distinguishable.

Therefore, when recording using the ink composition of the invention, animage can be formed with the desired metallic gloss, from a matte finishimage to a gloss finish image by appropriately combining images with ametallic gloss where the specular gloss measured at 20°, 60°, and 85° isno less than 200, 200, and 100 respectively, as measured on theaforementioned recording medium in accordance with JIS Z 8741.

On the other hand, if measurement values for the specular gloss at 20°,60°, and 85° does not exceed 200, 200, and 100, the image will not havea metallic glossy. feel when visually observed, but rather will appearto be gray. Furthermore, if the measured value for the specular gloss at20°, 60°, and 85° does not exceed any one of the aforementioned values,the effects of the invention will not be achieved.

From the perspective of ensuring the metallic gloss, the perspective ofprinting process, and the perspective of cost, the amount of inkcomposition that is sprayed onto the recording medium is preferablybetween 0.1 and 100 mg/cm², and more preferably between 1.0 and 50mg/cm².

The dry weight of the metallic pigment that forms an image on therecording medium is preferably between 0.0001 and 3.0 mg/cm², from theperspective of metallic gloss, printing process, and cost. A lower dryweight of the metallic pigment will provide a metallic glossy surfacewith high gloss. Therefore, this is suitable for forming a half mirrorimage on a transparent recording medium. Furthermore, if the dry weightof the metallic pigment is higher, a metallic glossy surface with amatte finish can be achieved. Therefore, this is suitable for forming ashielding layer on a transparent recording medium.

The method described below is suggested as a method for spraying the inkcomposition.

A first method is an electrostatic aspiration method, and is a system ofrecording by applying a strong electric field between a nozzle and anacceleration electrode placed in front of the nozzle, continuouslyspraying droplets of ink from the nozzle, and while the ink droplets aretraveling between the deflecting electrodes, applying a printinginformation signal to the deflecting electrode, or a system of sprayingink droplets corresponding to the printing information signal withoutdeflection.

A second method is a method of forcefully spraying ink droplets bymechanically vibrating a nozzle using a water crystal oscillator whileapplying pressure on the ink solution using a small pump. The inkdroplets that are sprayed are electrically charged while being sprayed,a printing information signal is applied to a deflecting electrode whilethe ink droplets are traveling between the deflection electrodes.

A third method is a system that uses a piezoelectric element, whererecording is performed by simultaneously applying pressure and aprinting information signal to the ink solution using a piezoelectricelement, and spraying the ink droplets.

A fourth method is a method where the ink solution is suddenly expandedin volume by the effect of thermal energy, and uses a system whererecording is performed by heating an ink solution to form bubbles usingan ultra-small electrode in accordance with a printing informationsignal, and spraying the ink droplets.

Any of the aforementioned methods can be used with the inkjet recordingmethod of this embodiment, but the method of spraying the inkcomposition without heating is preferable from the perspective ofprinting at high speed. In other words, the first method, second method,or third method are preferably used.

The recording medium is not particularly restricted, and for example,various types of recording media can be used, such as normal paper,special inkjet paper (matte paper, glossy paper), glass, plastic filmsuch as polyvinylchloride, film where a substrate is coated with aplastic or reception layer, metal, or printed circuit boards or thelike.

If the recording medium has an ink reception layer, the recording mediumis preferably printed without heating, from the perspective of avoidingheat damage.

On the other hand, from the perspective of achieving a high gloss, ifthe recording medium does not has an ink reception layer, the recordingmedium is preferably heated and printed.

The method of heating can be a method of heating by bringing therecording medium into contact with a heating source, or irradiating withinfrared rays or microwaves (electromagnetic waves with extremely largewave length of approximately 2,450 MHz) or the like, or heating byblowing hot air without contacting the recording medium, and the like.

The heating is preferably performed prior to printing and/or duringprinting and/or after printing. In other words, the recording medium canbe heated prior to printing, at the same time as printing, or afterprinting, or heating can be performed throughout the printing process.The heating temperature is dependent on the type of recording medium,but is preferably between 30 and 80° C., more preferably between 40 and60° C.

With the ink composition of the invention, recording can be performedusing the aforementioned inkjet recording method. The recorded mattercan be obtained using an ink set that includes the aforementioned inkcomposition, and therefore recorded matter can be obtained which has ahigh metallic mirror gloss with a specular gloss at angles of 20°, 60°,85° of no less than 200, 200, and 100 respectively. Furthermore, theconcentration of metallic pigment in the ink compositions that make theink set varies for each ink composition, and therefore arbitrary levelsof metallic gloss, ranging from mirror gloss to matte finish, can besimultaneously formed.

EXAMPLES Example A 1. Preparation of Metallic Pigment Dispersion

A resin coating solution containing 3.0 wt % of cellulose acetatebuterate (butylation ratio between 35 and 39%, manufactured by KantoChemical Co., Inc.) and 97 wt % diethylene glycol diethyl ether(manufactured by Nippon Nyukazai Co., Ltd.) was uniformly applied by abar coating method onto a 100 μm thick PET film, and then dried for 10minutes at 60° C. to form a thin resin film on a PET film.

Next, an aluminum vapor deposition layer with an average thickness of 20nm was formed on the aforementioned resin layer using a vacuumdeposition device (vacuum deposition device model VE-1010 manufacturedby Vacuum Device Co.).

Next, the multilayer body formed by the aforementioned method wassimultaneously peeled, pulverized, and dispersed in the diethyleneglycol diethyl ether using a VS-150 ultrasonic disperser (manufacturedby As One Corporation), and a metallic pigment dispersion was formed byultrasonically dispersing for 12 cumulative hours.

The metallic pigment dispersion that was obtained was filtered using anSUS mesh filter with 5 μm openings to remove the coarse particles. Next,the filtrate was poured into a round bottomed flask and the diethyleneglycol diethyl ether was distilled off using a rotary evaporator.Thereby the metallic pigment dispersion was concentrated, and later theconcentration of the metallic pigment dispersion was adjusted to obtaina metallic pigment dispersion 1 with a concentration of 5 wt %.

Furthermore, metallic pigment dispersions 2 through 11 were preparedusing metallic pigment where the vapor deposition conditions and/or theultrasonic dispersing time were changed.

Furthermore, the 50% average particle diameter R50 of a correspondingcircle in the longitudinal diameter (X direction)−lateral diameter (Ydirection) plane of each of the metallic pigments and the averagethickness Z were measured using a particle diameter and graindistribution analyzer (FPIA-3000S manufactured by Sysmex Corp.), andR50/Z was calculated based on the measurement values obtained for R50and Z. Note, the particle size distribution (CV value) was determined bythe equation CV value=standard deviation of the particle sizedistribution/average particle size×100. The results are shown in Table1.

TABLE 1 50% Average average Particle particle Average Metallic particlesize diameter film pigment diameter distribution Rmax thickness Zdispersion R50 (μm) (CV value) (μm) (μm) R50/Z 1 1.03 44.0 4.9 0.02 51.52 1.43 48.9 6.9 0.02 71.5 3 2.54 47.2 7.2 0.02 127.0 4 1.13 44.8 5.90.02 56.5 5 1.02 48.4 5.7 0.03 34.0 6 0.91 45.1 4.2 0.02 45.5 7 0.8646.6 4.3 0.02 43.0 8 0.89 38.2 3.2 0.02 44.5 9 5.52 81.2 30 0.10 55.2 101.42 65.0 12 0.30 4.7 11 1.40 60.2 7.1 0.30 4.7

2. Preparation of the Metallic Pigment Ink Composition

Metallic pigment ink compositions were prepared according to theformulations shown in Table 2 and Table 3 using the metallic pigmentdispersion that was prepared by the aforementioned method. Afterblending and dissolving the solvent and additives to make the inksolvent, the metallic pigment dispersion was added to the ink solvent,and then blended and stirred using a magnetic stirrer for 30 minutes atambient temperature and pressure to make a metallic pigment inkcomposition.

The diethylene glycol diethyl ether (DEGDE), dipropylene glycolmonobutyl ether (DPGMB), and tetraethylene glycol dimethyl ether (TEGDM)shown in Table 2 and Table 3 are manufactured by Nippon Nyukazai Co.Ltd. Furthermore, the γ-butyrolactone is manufactured by Kanto ChemicalCo. Inc. In addition, the N-2043-60MEX and N-2043-AF-1 (resin emulsion)is manufactured by Harima Chemical Co. Inc., and the BYK-3500(surfactant) is manufactured by BYK Japan. Note, the units are in wt %.

TABLE 2 Comparative Ink Example example Composition 1 2 3 4 5 6 7 8 1 23 DEGDE 47.8 47.8 47.8 61.8 61.8 61.8 61.8 61.8 47.8 47.8 47.8 GPGMB 4545 45 45 45 45 γ-butyrolactone 15 15 15 15 15 TEGDM 18 18 18 18 18N-2043-AF-1 6.0 6.0 6.0 4.0 4.0 4.0 4.0 4.0 6.0 6.0 6.0 BYK-3500 0.200.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 Pigment solid 1.0 1.01.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 content (metallic (1) (2) (3) (4)(5) (6) (7) (8) (9) (10) (11) pigment dispersion)

TABLE 3 Example Ink Composition 11 12 13 14 DEGDE 47.8  61.8 61.3 63.8GPGMB 45   — — — γ-butyrolactone — 15.0 15.0 15.0 TEGDM — 18.0 18.0 18.0N-2043-60MEX 6.0  4.0  4.0  2.0 BYK-UV3500  0.20  0.20  0.20  0.20Pigment solid 1.0  1.0  1.5  1.0 content (metallic pigment (8)   (8) (8)  (8)  dispersion)

3. Evaluation Test (1) Spray Stability

A black block was filled with an ink composition using an inkjet printerEM-930C (manufactured by Seiko Epson Corp.), and solid fill printing wasperformed at ambient temperature on photographic paper (glossy)manufactured by the same company (Product Number: KA450PSK).

At this time, the inkjet printer nozzle diameter (L) was 25 μm, and thesize of the openings (W) of the mesh filter in the ink flow path was 5μm. Therefore, the inkjet printer that was used had a relationship whereL=5W. Furthermore, a ratio (%) was calculated for the number ofplate-like particles where the relationship between the average particlediameter (R) of a corresponding circle determined from the surface areain the X-Y plane of the plate-like particles that were included in theink composition and the nozzle diameter (L) of the inkjet printersatisfied the condition of R>(L/5).

The solid fill printed image obtained was visually observed for thepresence of spray defects (nozzle skipping), and the spray stability wasevaluated according to the following evaluation criteria. Note, “nozzleskipping” refers to areas where ink should have been sprayed from anozzle on a normal print head but was not sprayed because of nozzleplugging, thus affecting the printing results. The evaluation resultsare shown in Table 3 along with the ratio (%) of the number ofplate-like particles satisfying the condition R>(L/5).

AA: Spray defects (nozzle skipping) did not occur even when continuouslyprinting an A4 size solid filled image on 30 consecutive sheets.

A: Spray defects (nozzle skipping) did not occur even when continuouslyprinting an A4 size solid filled image on 10 consecutive sheets.

B: Spray defects (nozzle skipping) occurred between the second and9^(th) sheets when a A4 size solid filled image was continuouslyprinted.

C: Spray defects (nozzle skipping) occurred on the first page whencontinuously printing an A4 size solid filled image.

(2) Gloss Measurement

A black block was filled with an ink composition using an inkjet printerEM-930C (manufactured by Seiko Epson Corp.), and solid fill printing wasperformed at ambient temperature on photographic paper with an inkreception layer (glossy) manufactured by the same company (ProductNumber: KA450PSK). The amount of ink composition that was sprayed atthis time was 1.2 mg/cm, and the dried weight of the metal pigment was12 μg/cm². The gloss of the image obtained was measured using a glossmeter (MULTI Gloss 268, manufactured by Konica Minolta Co., Ltd.). Theresults are shown in Table 4 and Table 5.

TABLE 4 Recording and printing R > L/5 Gloss stability (%) 20° gloss 60°gloss 85° gloss Example 1 A 1.2 283 363 107 Example 2 A 1.1 401 411 110Example 3 A 4.4 225 372 103 Example 4 A <0.1 895 604 125 Example 5 A<0.1 733 553 121 Example 6 A <0.1 560 547 124 Example 7 A <0.1 626 483120 Example 8 AA <0.1 663 506 123 Comparative C 50 — — — Example 1Comparative B 3.1 171 311 104 Example 2 Comparative B 4.3 333 409 116Example 3 —: Not detected

TABLE 5 Recording and printing R > L/5 Gloss stability (%) 20° gloss 60°gloss 85° gloss Example 11 AA <0.1 350 434 116 Example 12 AA <0.1 895604 125 Example 13 AA <0.1 782 592 125 Example 14 AA <0.1 940 604 128

(3) Evaluation of Thermal Printing

The ink composition of example 1 was filled in the yellow block using aninkjet printer SJ-540 (manufactured by Roland DG Corp.), and then solidfill printing and thermal printing was performed on a glossy polyvinylchloride film (with gray adhesive) which did not have an ink receptionlayer (product number: SP-SG-1270G). Next, the gloss of the imageobtained was measured using a gloss meter (MULTI Gloss 268, manufacturedby Konica Minolta Co., Ltd.). The results and the heating conditions areshown in Table 6. Note, the heating conditions are for the case whereheating to 40° C. was performed during printing (example 9) and for thecase where heating was performed in a dryer at 60° C. after printing atambient temperature (example 10). Furthermore, for comparison, the casewhere only ambient temperature printing was performed without heating(reference example) was also evaluated.

Similarly, an evaluation was also performed in a manner similar toexample 9 except that the ink composition of example 13 was used(example 15).

TABLE 6 (3) Thermal printing evaluation Heating 20° gloss 60° gloss 85°gloss conditions Example 9 260 405 120 40° C. during printing Example 10218 406 117 60° C. after printing Reference 99 214 68 No heating example

TABLE 7 (3) Thermal printing evaluation Heating 20° gloss 60° gloss 85°gloss conditions Example 15 275 408 116 40° C. during printing

Example B 1. Preparation of Metallic Pigment Dispersion

A dispersion containing a metallic pigment was prepared similar to

Example A.

2. Preparation of the Metallic Pigment Ink Composition

Metallic pigment ink compositions were prepared according to theformulations shown in Table 8 and Table 9 using the metallic pigmentdispersion that was prepared for example A. After blending anddissolving the solvent and additives to make the ink solvent, themetallic pigment dispersion was added to the ink solvent, and thenblended and stirred using a magnetic stirrer for 30 minutes at ambienttemperature and pressure to make a metallic pigment ink composition.

The diethylene glycol diethyl ether (DEGDE) and the tetraethylene glycoldimethyl ether (TEGDM) shown in Table 8 and Table 9 are manufacture byNippon Nyukazai Co. Ltd. Furthermore, the γ-butyrolactone wasmanufactured by Kanto Chemical Co. Inc. In addition, the N-2043-60MEXand N-2043-AF-1 (resin emulsion) are manufactured by Harima Chemical Co.Inc., and the BYK-3500 (surfactant) is manufactured by BYK Japan. Note,the units are in wt %.

TABLE 8 Comparative Ink Examples Examples Composition 16 17 18 19 20 4 56 DEGDE 64.30 64.05 63.80 63.30 62.80 64.05 63.80 62.80 γ-butyrolactone15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 TEGDM 18.0 18.0 18.0 18.0 18.018.0 18.0 18.0 N-2043-AF-1 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 BYK-3500 0.20.2 0.2 0.2 0.2 0.2 0.2 0.2 Pigment solid 0.50 0.75 1.00 1.50 2.00 0.751.00 2.00 content (metallic (4) (4) (4) (4) (4) (10) (10) (10) pigmentdispersion)

TABLE 9 Examples Ink Composition 21 22 23 DEGDE 64.05 63.80 63.30γ-butyrolactone 15.0  15.0  15.0  TEGDM 18.0  18.0  18.0  N-2043-60MEX2.0 2.0 2.0 BYK-3500 0.2 0.2 0.2 Pigment solid  0.75  1.00  1.50 content(metallic pigment (8)   (8)  (8)  dispersion)

3. Evaluation Test (1) Gloss Measurement

A black block was filled in with an ink composition using an inkjetprinter EM-930C (manufactured by Seiko Epson Corp.), and solid fillprinting was performed at ambient temperature on photographic paper withan ink reception layer (glossy) manufactured by the same company(Product Number: KA450PSK). The amount of ink composition that wassprayed at this time was 1.2 mg/cm², and the dried weight of the metalpigment was 12 μg/cm². The gloss of the image obtained was measuredusing a gloss meter (MULTI Gloss 268, manufactured by Konica MinoltaCo., Ltd.). Furthermore, functional evaluation of the printed matter wasbased on the following evaluation standard. The results are shown inTable 10 and Table 11.

AA: Mirror gloss (a reflected object can easily be determined.Sharpness)

A: Glossy (A metal gloss is observed, but there is no sharpness.)

B: Matte finish (metallic gloss with no shine)

C: Gray finish (Metal gloss is not observed, and appearance is gray.)

TABLE 10 Gloss 85° Functional Evaluation of 20° gloss 60° gloss glossPrinted Matter Example 16 331 345 118 B Example 17 698 510 123 AAExample 18 895 604 125 AA Example 19 782 592 125 AA Example 20 531 512120 A Comparative 158 286 102 C example 4 Comparative 171 311 104 Cexample 5 Comparative 117 301 106 C example 6

TABLE 11 Gloss Functional Evaluation of 20° gloss 60° gloss 85° glossPrinted Matter Example 21 910 571 124 AA Example 22 940 604 128 AAExample 23 826 595 126 AA

From the above results, it can be seen that the ink compositions(examples 16 through 20) used in the ink set of the invention can forman image with different levels of metal gloss according to theconcentration of metallic pigment. Therefore, an ink set that containsink compositions with different concentrations of metallic pigment cansimultaneously print printed matter which has a high metallic mirrorgloss with a specular gloss at angles of 20°, 60°, and 85° of 200, 200,and 100 or higher, respectively, and which has gloss ranging from mirrorgloss to a matte finish.

1. An ink composition comprising a metal pigment, wherein the metalpigment contains plate-like particles, and in the case where thelongitudinal diameter on the planar surface of the plate-like particleis X, the lateral diameter is Y, and the thickness is Z, the 50% averageparticle diameter R50 of a corresponding circle determined from thesurface area in the X-Y plane of the plate-like particle is between 0.5and 3 μm, and the condition R50/Z>5 is satisfied; and when applied to aninkjet recording device that satisfies the condition of L≧5W where L μmis the nozzle diameter of an inkjet head and W μm is the size of a meshfilter opening provided in an ink flow path, the number of plate-likeparticles where the average particle diameter R μm of a correspondingcircle determined from the surface area in the X-Y plane of theplate-like particles satisfies the condition R>(L/5) being no more than5% of the total number of plate-like particles.
 2. The ink compositionaccording to claim 1, wherein the maximum particle diameter Rmax of acorresponding circle determined from the surface area in the X-Y planeof the plate-like particles is 10 μm or less.
 3. The ink compositionaccording to claim 1, wherein the metal pigment is aluminum or analuminum alloy.
 4. The ink composition according to claim 1, wherein themetal pigment is made by crushing a metal deposition film.
 5. The inkcomposition according to claim 1, wherein the particle size distributionCV value of the metal pigment as determined by the following Equation 1is 60 or less:CV value=standard deviation of particle size distribution/averageparticle diameter×100.   Equation 1
 6. The ink composition according toclaim 1, wherein the concentration of the metal pigment in the inkcomposition is between 0.1 and 3.0 wt %.
 7. The ink compositionaccording to claim 1, further comprising an organic solvent and a resin.8. The ink composition according to claim 7, wherein the organic solventincludes one or more type of alkylene glycol ether that is a liquid atambient temperature and pressure.
 9. The ink composition according toclaim 7, wherein the organic solvent is a blend of an alkylene glycoldiether, an alkylene glycol monoether, and a lactone.
 10. The inkcomposition according to claim 7, wherein the resin is at least one typeof resin selected from a group consisting of polyvinyl butyral,cellulose acetatobutyrate, and polyacryllic polyol.
 11. The inkcomposition according to claim 1, further comprising at least one typeof acetylene glycol based surfactant and/or silicone based surfactant.12. An ink set, comprising a plurality of the ink compositions accordingto claim 1, wherein each of the ink compositions has a differentconcentration of metal pigment.
 13. The ink set according to claim 12,wherein the concentration of a metal pigment in at least one of the inkcompositions is 0.1 wt. % or higher and less than 1.5 wt %, and theconcentration of a metal pigment in at least one of the other inkcompositions is 1.5 wt. % or higher and 3.0 wt % or less.
 14. Arecording device, comprising the ink set according to claim 12.